In commonly owned copending U.S. application Ser. No. 8,091, filed Jan. 31, 1979 by one of us, Guido Busacca, jointly with three others, there has been described a mechanism for the purpose set forth in which an annular tuning piston axially displaceable in the cylindrical cavity of a magnetron of the coaxial type is coupled with an eccentric portion of a rotating crankshaft via a pitman whose length is related in a predetermined manner to the eccentricity of the crankshaft in order to linearize the relationship between the operating frequency of the oscillator and the displacement of the crankshaft drive as determined by a position sensor. The extremity of the pitman remote from the crankshaft axis is articulated to a linearly guided yoke rigid with the tuning piston.
Whereas the operation of this earlier tuning mechanism is generally satisfactory, friction inevitably occurs at the articulated joint between the yoke and the pitman as the latter executes a motion with a transverse component. This friction is a cause of wear at the joint itself as well as along the guide surfaces of the piston rod subjected to lateral stresses by that transverse component of motion.